<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    div {
      width: 80px;
    }

    input[type=text] {
      width: 50px;
      height: 44px;
      outline: none;
      border: 1px solid #ccc;
      text-align: center;
      border-right: 0;
    }

    input[type=button] {
      height: 24px;
      width: 22px;
      cursor: pointer;
    }

    input {
      float: left;
      border: 1px solid #ccc;

    }
  </style>
</head>

<body>
  <div>
    <input type="text" id="total" value="0" readonly>
    <input type="button" value="+" id="add">
    <input type="button" value="-" id="reduce" disabled >

    <script>

      const text = document.querySelector(`#total`);
      const add = document.querySelector(`#add`);
      const reduce = document.querySelector(`#reduce`);

      add.addEventListener('click', function () {
        text.value++;
        if (text.value > 0) reduce.disabled = false;
      })


      reduce.addEventListener('click', function () {
        text.value--;
        if (text.value == 0) reduce.disabled = true;
      })

    </script>

  </div>
</body>

</html>